Removing rvm 2.0.0 tests due to Nokogiri 1.7.0 update

[alvin-huang]

Travis tests are failing with

Gem::InstallError: nokogiri requires Ruby version >= 2.1.0.
Installing rb-inotify 0.9.7
An error occurred while installing nokogiri (1.7.0), and Bundler cannot
continue.
Make sure that `gem install nokogiri -v '1.7.0'` succeeds before bundling.

due to the 1.7.0 release of nokogiri on 12-26-2016, which removed support for ruby 1.9.2, 1.9.3, and 2.0.0 (see CHANGELOG)

A more detailed PR for the nokogiri 1.7.0 release is here

[alvin-huang]

Instead of this change we can make some changes in the Gemfile instead.

[truthbk]

@alvin-huang thanks for taking the time to find the root cause 🥇 We probably don't want to drop our support for 2.0.0 testing just yet (although we've considered this a couple of times already). We can probably pin nokogiri to ~> 1.6.0, that should probably do it as well.

[truthbk]

Merged in #298 which just pinned the version. We might eventually remove the 2.0.0 support after the next major release, but we can't do that right now without risking breaking older puppets. Thank you for work, although I'm closing this was super helpful. 🙇